Electrical current-limiting fuse



July 27, 1965 E. LANGE ETAL 3,197,593

ELECTRICAL CURRENT-LIMITING FUSE Filed April 20, 1961 FIG. 2. FIG. I.

FIG. 4. FIG. 3.

United States Patent 3,197,593 ELECTRICAL CURRENT-LIMITING FUSE EmilLange, Ville-dAvray, France, and Bernt Ingvaldsen,

Dramlnen, Norway; said Ingvaldsen assignor to Aktieselslrabet N ationaiIndustri, Drammen, Norway Filed Apr. 20, 1961, Ser. No. 104,480 1 Claim.(Cl. 200135) This invention relates to electric safety fuse componentsof the kind comprising fusible metallic conductors and non-metallicmaterial.

There are known fuse components of the kind referred to which eachcomprise a fuse wire arranged in an insulating tube which is filled withsand. The volume of the sand is very large in proportion to that of thefuse wire, and because of this the construction of the fuse component isunduly large and expensive.

The necessity of a large volume of sand in such hitherto known fusearrangements is due to the need for a safe manner of operation ininterrupting an electric current. The sand loosely surrounds the fusewire, and because of this the process of interrupting the current isoften inefiicient so that the fuse arrangement is damaged by explosion.

The invention is intended to provide an improved fuse component of thekind referred to in which the fuse wire is not loosely embedded in sandor other non-metallic material and the latter is not present in undulylarge quantities.

According to the invention there is provided an electric safety fusecomponent comprising a fusible metallic conductor and non-metallicmaterial, characterised in that the metallic conductor is directly infixed connection with a pre-determined volume of the non-metallicmaterial. The non-metallic material may consist of or comprise sand. Inone advantageous construction the metallic conductor is in the form of awire or strip on the surface of which the non-metallic material iscarried in the form of a layer or covering of a pre-determined quantityor thickness. In a modified construction the metallic conductor istubular and non-metallic material is provided both inside and outsidethe metallic conductor. Sand or other non-metallic material may bedistributed throughout the metal of the metallic conductor, and the fusecomponent may comprise or be surrounded by a thinwalled tube ofinsulating material. When sand is used it may be fine-milled.

The invention is illustrated by way of example in the accompanyingdrawing, in which FIGURES 1, 3, 5 and 7 show four fuse componentsaccording to the invention in longitudinal section, and

FIGURES 2, 4, 6 and 8 are cross-sectional views correspondingrespectively to FIGURES 1, 3, 5 and 7.

FIGURES l and 2 show a fuse component comprising a metallic conductor inthe form of a wire 1 0n the surface of which non-metallic material iscarried in the form of a layer 2 of sand of a pre-determined quantity orthickness directly in fixed connection with the wire 1. The thickness ofthe layer 2 of sand may be between 0.1 and 4 millimetres and isdetermined in accordance with the desired current breaking capacity ofthe fuse component. In particular instances this thickness and thus thevolume of the sand may be still greater.

In order to apply the sand directly in fixed connection on the metallicconductor, the sand may, for example, be mixed with a suitable liquid orbinder and applied in ice the form of a paste or mixture which hardensupon the conductor, so that the latter is then enclosed or surrounded bya fixed layer of sand. It is also possible to apply the sand to themetallic conductor whilst the latter is heated so that it glows; whenusing such a process the sand layer fixedly surrounds the conductor andsome sand particles penetrate the conductor.

In order to protect the layer of sand from external influences a verythin-walled tube of insulating material may be drawn over the layer ofsand. This arrangement has the advantage that it is possible to use atube of insulating material which generates gas to assist the breakingof the current.

The device operates as follows:

Upon the occurrence of an excessive current or shortcircuit current thefuse wire which is surrounded with sand melts through and the sandimmediately in its vicinity is likewise fused so that the currentbreaking process proceeds until the flow of current is terminated. Afterthis process the melted layer of sand remains behind.

The construction of fuse arrangements can be greatly simplified by theuse of fuse wires with fixed sand coverings. The manner of operation ofsuch a fuse arrangement is in no Way influenced disadvantageously andits capacity lies within the same limits as with the known fusearrangements. Because of the prior determination of the thickness of thesand covering it is easy to determine in advance the capacity of thedevice.

In order to achieve a still better effect from the melting sand, themetallic conductor 3 may be tubular with non-metallic material 4 insideand non-metallic material 2 outside as shown in FIGURES 3 and 4. Thesand provided both internally and externally operates very favourablyduring the fusing process.

FIGURES 5 and 6 illustrate how a still more intimate connection may beachieved between the metal of the conductor 5 and the sand bydistributing the non-metallic material throughout the metal by castingthem together. Such a mixture permits a very favourable fusing processbetween the metal and the sand.

FIGURES 7 and 8 illustrate how a fuse wire 1 with a sand covering 2 canbe surrounded by a thin-Walled tube 6 of insulating material. Thisarrangement has the advantages that the layer of sand is well protectedand that during the fusing process gases released from the material ofthe tube can co-operate favourably in the quenching process.

The fuse wire with a fixed sand covering can be used with substantialadvantages in many fuse arrangements.

An example of a suitable use of fuse components in accordance with theinvention is in fuse arrangements of the kind in which quenching of thearcs is effected by means of a stream of quenching material underpressure generated by the arcs themselves. In such fuse arrangementswith conventional fuse wires, especially for very high voltages, with aview to the interruption of small currents the length of theconstruction must be made very large and consequently it is necessary toquench a long arc. In the interruption of large currents however thislong burning arc produces in the quenching chamber a pressure which isunnecessarily high but makes a very heavy construction of the quenchingchamber necessary.

By the use of a fuse wire With a sand covering of quite small thicknessit is easily possible to interrupt the small currents because of theaction of the sand. Thus the fuse arrangement can be reduced to smalldimensions so that the interruption of large currents is effectedWithout the production of excessive increases in pressure in thequenching chamber through the streams of quenching medium flowing underpressure produced by the arcs themselves.

The sand may be fine-milled to the form of powder and then mixed with aliquid to form a paste to be applied to the fuse Wire. The mixturehardens and surrounds and encloses the fuse Wire completely so that thematerials necessary for the current breaking process are employed veryadvantageously.

We claim:

In an electric current-limiting fuse consisting of a fusiforming a fixeduniform hard coating enclosing said conductor, the fuse structure withsome of said sand penetrating the surface of said conductor resultingfrom heating said conductor and said sand together.

References Cited by the Examiner UNITED STATES PATENTS ble metallicconductor and sand, with some of said sand 15 B RN RD A. ILHEANY,Primary in r.

